1. Field of the Invention
The present invention pertains to a pressure plate assembly of the type including a housing; a pressure plate, which is installed in the housing and which is connected by a connecting arrangement to the housing so that it can rotate in common with the housing around an axis of rotation and also move in the direction parallel to the axis of rotation; a force-exerting arrangement, which is supported against the housing and the pressure plate, by means of which arrangement force can be exerted on the pressure plate to produce an engaged state; and a wear take-up device with at least one adjusting element, which is under the pretensioning force of a pretensioning arrangement so that adjusting processes can be carried out.
2. Description of the Related Art
A pressure plate assembly of this type, which is used in friction clutches for motor vehicles, is known from U.S. Pat. No. 4,207,972. In this known pressure plate assembly, the wear take-up device comprises a ring-like adjusting element, which is pretensioned by the force of a pretensioning spring to rotate in the circumferential direction. Complementary ramp surfaces are provided on the adjusting element and on the pressure plate, so that, when the adjusting element rotates, its ramp surfaces slide over the complementary ramp surfaces of the pressure plate. As a result, the area on the adjusting element which contacts an energy-storage device is shifted in the axial direction with respect to the pressure plate. It is possible in this way to compensate for the wear which occurs during operation. That is, when a clutch-release operation is performed, the pressure plate, upon which a releasing force-producing arrangement acts, first follows along with the clutch-release movement of the energy-storage device but then stops when a release distance-limiting arrangement goes into effect. The energy-storage device thus has no more actuating effect even though its release movement continues. The wear take-up process continues until the adjusting element comes to rest again on the energy-storage device, which is held in its released position.
These types of pressure plate assemblies, which are used primarily in trucks, lead during operation to the problem that, during the time that the pressure plate is pretensioned for at least a certain period by the releasing force-producing arrangement against the energy-storage device during a clutch-release operation, impacts can cause the pressure plate to move in the axial direction; this axial movement moves the pressure plate against the force of the releasing force-producing arrangement and thus away from the energy-storage device. This can occur, for example, when a truck is driving in reverse and hits a loading ramp. The result is that the clamping effect is briefly released, and an undesired wear take-up adjustment can thus occur in the pressure plate assembly. The energy-storage device will then assumes a more-or-less undefined position.